The final report has just been published on the Department of Energy (DOE)-funded project in central Texas that focused on the use of dynamic line rating (DLR) to provide real-time information on conductor temperature, enabling system operators to make fully informed decisions on how hard they can drive their overhead power lines.
Oncor, a U.S. transmission and distribution utility, successfully completed a DOE Smart Grid Demonstration Program (SGDP) showing that the real-time information provided by Nexans’ DLR technology can make an important contribution to increasing the power-carrying capacity of existing overhead line assets and reducing congestion.
For the core component of the SGDP, Oncor installed the DLR technology on eight 138-kV to 345-kV transmission circuits in central Texas, where it enabled power capacity to be increased by up to 14 percent.
The Nexans DLR technology employs an algorithm that transforms real-time sensor data into a conductor temperature and calculates the maximum current capacity — the DLR — which maintains the overhead line sag within safe clearance limits. The DLR is updated every five to 10 minutes, providing operators with much clearer visibility than both traditional static line ratings, which use predetermined weather assumptions, and ambient-adjusted ratings, which take into account the ambient air temperature.
The final report states, “The SGDP Project has been a complete success, having demonstrated that Dynamic Line Ratings are a practical and efficient tool to increase the capacity of a transmission line, which will enable transmission providers and system operators to mitigate congestion, increase system reliability and redeploy capital to its most efficient uses through a least regrets strategy.”
DLR was being evaluated as a potential key component of Oncor’s five-year capital investment program that will average $1 billion per year. The program’s strategy is to invest in technologies and equipment to improve reliability and efficiency of the company’s infrastructure.
“Our investment program is not about just adding more infrastructure,” said Jim Greer, Oncor chief operating officer. “We want to be able to use our existing assets more efficiently and effectively because that’s a more economical use of our investment dollars. DLR clearly demonstrated that we could improve the efficiency of our existing assets in an economical manner. Already we are looking at other areas of our grid where we can install this capability for future investments. This is good for Oncor, the state grid and ultimately all of the customers we serve.”
The report highlights the following:
- Increased line capacity. DLR provided up to 14 percent additional capacity above the ambient temperature-adjusted ratings. The incremental capacity was available from 83.5 to 90.5 percent of the time.
- Reduced congestion. The project found that 5 percent additional capacity could relieve congestion by up to 60 percent on the target lines with DLR installed, while 10 percent additional capacity would practically eliminate all congestion on the target lines. Congestion on the Oncor transmission lines in 2011 and 2012 cost more than $148 million and $197 million respectively.
- Market integration. The integrated DLR (iDLR) system at Oncor feeds real-time conductor ratings to the Electric Reliability Council of Texas (ERCOT), the market operator, which then incorporates the additional capacity into its Security Constrained Economic Dispatch process. With zero operator intervention, DLR capacity is used to increase market efficiency.
- Transmission planning. By providing additional capacity on transmission lines where a full upgrade cannot yet be justified, DLR can be used in the planning process to enable a least-regrets capital strategy.
Best practices. The project authors have developed a guide to assist other transmission owners who are considering DLR technology for their own systems.
As evidence of the extensibility of DLR technology, in June 2013 Oncor deployed additional DLR systems in the Odessa-Midland region of Texas in a commercially funded follow-on project.